Manufacture of nitrocellulose



Patented Nov. 3, 1936 UNITED STATES MANUFACTURE OF NITROCELLULOSE Roderick K. Eskew, Portland, Maine, assignor, by

mesne assignments, to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application March 2, 1935, Serial No. 9,123

3 Claims.

This invention relates to the manufacture of nitrocellulose and, more particularly, to a process in which the source of cellulose is dense wood pulp.

Heretofore, the manufacture of nitrocellulose from dense wood pulp has been carried out. The

wood pulp sold for this purpose is of high whiteor 75. The compactness of sheets of cellulose is expressed in this manner throughout the present specification.

In the heretofore proposed processes of manufacturing nitrocellulose from sheets of compact cellulose, the nonuniformity of the resulting product has been objectionable. A further objectionable feature is the uneconomical nature of such processes, either with respect to the time involved for the complete cycle or the excessive nitric acid consumed.

An object of the present invention is to provide a process of manufacturing nitrocellulose of the highest uniformity and of the desired nitrogen content from dense cellulose pulp. A further object is to provide such a process that will be economical and have a short time cycle. Other objects of the invention will be apparent from the description given hereinafter.

The above obj ectsareaccomplished according to the present inventionbygranulating sheets of cellulose pulp having a thickness of .020.080" and a compactness of 50-115 into chips and nitrating the chips so produced with a mixed acid composition containing 50-75% nitric acid together with sulphuric acid and Water.

It is known that economies in nitrating cellulose are effected by employing a mixed acid composition having a relatively high nitric acid content and by the use of a relatively small quantity of the mixed acid, for example, an amount of mixed acid equal to 8-10 times the dry weight of the cellulose used- A so, that obvious economies are effected by using cellulose in dense form instead of in the form of thin waterleaf tissue or disintegrated into its ultimate fibers. However, despite the saving in time and ease of handling the cellulose by adopting these relatively recent suggestions in the art, there are serious objections which can only be overcome or reduced to a minimum by carefully balancing the various factors involved in the nitrating process.

It has been found that, to devise an economical process of manufacturing nitrocellulose of high uniformity from dense cellulose pulp, it is of the greatest importance to carefully balance the thickness of the sheet of cellulose pulp, its compactness, and the concentration of nitricacid in the mixed acid composition in which the nitrating is carried out.

By observing the conditions set forth above, it is possible to nitrate economically dense cellulose chips using a relatively small proportion of mixed acid to cellulose chips, in a period of approximately an hour and to' obtain a uniformly nitrated product still in chip form without physical disintegration or degradation of the cellulose or gelatinization of the surface of the chips. Furthermore, such a product may be readily stabilized by the conventional purification treatment given nitrocellulose after nitration.

More particularly, the present invention is 30 carried out by granulating, without disintegrating, a sheet of cellulose pulp having a thickness of .030-.035" and a compactness of 50-115, preferably a compactness of -80, into chips about to square and nitrating the chips so produced with a mixed acid composition containing about 60% nitric acid together with sulphuric acid and water at a temperature of 4050 C., the amount of mixed acid used being preferably about ten times the dry weight of the cellulose.

In order to illustrate the invention, the following examples are given:

Example 1.--Highly purified wood cellulose of about 94% alpha cellulose content, in the form of sheets .035 thick and having a compactness 45 of 80, were cut into chips x by means of a machine of the general type of a Ballistite cutter. The object of this step is to avoid disintegrating the sheet but to granulate it into uniformly sized and cleanly cut units convenient for handling and susceptible to penetration by the nitrating acid.

After drying the chips to about 1% moisture content, 1'75 pounds of the chips were immersed with continuous stirring in ten times their weight of a mixed acid composition as follows:

Percent Nitric acid 60.0 Sulphuric acid 27.0

Water 13.0

The initial temperature of the acid was about 40 C. and as the reaction proceeded it reached about 52 C. The nitration was carried out in an ordinary mechanical type dipper pot of a design well known in the industry. The mixture was agitated continuously and the reaction was permitted to continue for one hour, at the end of which time the charge was dropped into a centrifuge and the excess spent acid was wrung out. The nitrocellulose was then drowned in a large excess of water and stabilized in the ordinary manner by heating for about six hours in acidulated Water and then washing acid free.

The finished product was a uniformly nitrated nitrocellulose of about 11% nitrogen content, well suited for use in making camphor-alcohol plastics, and the like.

Example 2.In this example the procedure was carried out as in Example 1 except that the cellulose sheet from which the chips were cut 'had a compactness of about 110 and the mixed acid composition was as follows:

, Percent Nitric acid 60.0 Sulphuric acid 29.0 Water 11.0

The finished nitrocellulose had a nitrogen content of about 12% and was well adapted for use in metal and wood finish lacquers, leather dopes,

and the like.

It is to be understood that the above examples are merely illustrative and the process of the present invention may be carried out within the limits herein disclosed. While it is economical to use a mixed acid composition having a. nitric acid content in the lower part of the 50-75% range, because of the decreased cost of fortifying the spent acid with highly concentrated nitric acid for reuse, this is to some extent counterbalanced by the advantages of using a cellulose sheet of high compactness. To get a, uniformly nitrated product employing a cellulose sheet of high compactness, for example, above about 80, it is necessary to use a mixed acid composition having a nitric acid content in the higher part of the 50-75% range. Although the use of this relatively high percentage of nitric acid increases the expense of fortifying the spent acid, yet an advantage is gained in using this cellulose sheet of high compactness because it permits the use of lower ratios of mixed acid composition to chips and gives better yields. Also, the more compact cellulose will not be disintegrated, nor contaminate the mixed acid composition, as is the tendency of a cellulose of loW density.

Applicant has found that, by observing the conditions herein set forth, the nitration of dense cellulose with a nitrating acid having a relatively high nitrogen content can be economically and satisfactorily effected using quite low ratios of mixed acid composition to cellulose in quite short periods in the neighborhood of an hour or so.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. Process comprising granulating a sheet of cellulose pulp having a thickness of .020-.080 and a compactness of 50-115, into chips approximately to 1 square and nitrating said chips with a mixed acid composition containing 50-75% nitric acid together with sulphuric acid and water, at a temperature of not substantially less than 40 C., the amount of mixed acid composition being approximately 10 times the dry weight of said chips.

2. Process comprising granulating a sheet of cellulose pulp having a thickness of 030-035" and a compactness of 50-115, into chips approximately to square and nitrating said chips with a mixed acid composition containing about 60% nitric acid together with sulphuric acid and water, at a temperature of 40-50 C., the amount of mixed acid composition being approximately 10 times the dry Weight of said chips.

3. Process comprising granulating a sheet of cellulose pulp having a thickness of .030-.035 and a compactness of 60-80, into chips approximately x and nitrating said chips with a mixed acid composition containing about 60% nitric acid together with sulphuric acid and water, at a temperature of 40-50 C., the amount of mixed acid composition being approximately 10 times the dry Weight of said chips.

RODERICK K. ESKEW. 

